A time master station and a plurality of time slave stations which are connected to a network include a clock, respectively. It is necessary to synchronize the times counted by the respective clocks. Therefore, techniques to synchronize the times have been proposed as disclosed in Patent Literatures 1 to 5. When respective units in the network system including the time master station and the time slave stations are synchronized with each other, not only cooperative-operation command information that indicates the start of cooperative operation, but also cooperative-operation time information that indicates a cooperative-operation time are provided to each of the units. Therefore, improvement in the reliability of the network system can be achieved. Further, there is a demand for a technique to provide correct cooperative-operation time information even when synchronization jitter causes a synchronization error between a time counted by the clock of the time master station and a time counted by the clock of the time slave station, and thus improve the reliability of the network system.